In a mobile communication, the quality of a received signal deteriorates extremely due to fading. One of effective methods for overcoming the fading is a diversity technique. The diversity technique usually uses a plurality of received signals to achieve transmission of high communication quality. For example, when a receiver has two antennas spaced adequately apart from each other, the fading variation on the antenna is independent of each other. Accordingly, provability decreases that the power of signals received by the two antennas decreases at the same time. The diversity technique uses such a principle to prevent the power of a received signal from falling down on a receiver side.
There are, however, various restrictions to achieve the diversity in a communication terminal apparatus such as a mobile station. Therefore, in order to achieve the diversity, which should be achieved originally on a receiver side in the mobile station, on a transmitter side of a base station, a transmit diversity technique has been investigated.
In the transmit diversity, as illustrated in FIG. 1, base station 1 transmits signals with the same phase to mobile station 3 using antennas 2a and 2b, and mobile station 3 selects a received signal transmitted from one of the antennas with a power level larger than that of the other signal. Due to the transmit diversity, it is possible to suppress the effect of fading, and to improve the communication quality.
In the transmit diversity, it is thus possible to suppress the effect of fading, and to improve the communication quality, however, it is not possible to provide interfering suppressing effect that is an effect for suppressing the interference in other stations. Particularly in a CDMA system, suppressing interference in other stations enables each station to perform efficient communications, further enables the system capacity to be increased. Therefore, the interfering suppressing effect becomes important.